1. Field of the Invention
The present invention relates to sensors and more particularly to sensors for determining when a hand brake has been released. The invention finds primary utility in determining when the hand brake of a railroad car has been released or is un-locked.
2. Description of the Prior Art
While the present invention will be described in connection with the brake system of a railroad car, its utility in other applications should be apparent. It is well known in the art of railroad car building to equip the cars with a manual brake system which is actuated by a manually turned brake wheel located on the car. Generally, the brake wheel is attached through gearing to an axel that is attached to a chain running down the car and generally to the undercarriage where the chain is linked to the brake rigging. Turning the brake wheel in a first direction, gathers the chain, putting it in tension, whereby the brakes of the car are engaged to prevent the car wheels from turning. Turning the brake wheel in the opposite direction unwinds the chain from the axel and removes the tension on the chain to disengage the brakes and allow the car wheels to turn. The railroad industry has very high maintenance costs related to wheel damage that may be caused by the brakes of a car being left engaged or xe2x80x9conxe2x80x9d when the train begins to move. If the hand brakes of a car are left on, the car wheels will not turn and damage in the form of a worn flat spot will result. In some cases, derailment of the car could even occur. It is therefore desirable to provide a sensor that will indicate the brake setting or, more particularly, will indicate when the brakes of a car are disengaged or xe2x80x9coffxe2x80x9d before the train is moved.
In a U.S. Pat. No. 6,170,619 B1, entitled xe2x80x9cManual Hand Brake Sensor For A Railroad Carxe2x80x9d by Alan V. Sheriff et al which issued Jan. 9, 2001 and is assigned to the assignee of the present invention, a system for determining that the hand brakes are xe2x80x9coffxe2x80x9d so that the train may be moved without the car wheels being locked, is described claimed. In this patent, a magnetic target is attached to a cam or gear which is driven by the turning of the brake wheel. As the brake wheel is turned to loosen the chain and release the brake, the target moves toward a magnetic sensor or Hall device, which is in a fixed position. When the target is within the sensitivity of the magnetic sensor, a signal is generated to indicate that the brake is xe2x80x9coffxe2x80x9d and the train may be moved. While this invention operates quite satisfactorily, it is somewhat cumbersome to install on the already existing equipment of the car. For example, the protective box around the mechanism must be opened and the sensor and target installed therein. Furthermore, the sensor is attached to the already existing gears in the brake system and the exact location of the sensor and the target must be determined, usually by trial and error until the desired location is found to assure that the signal produced is truly indicative of an xe2x80x9coffxe2x80x9d condition. Also, because the brake wheel is turned approximately five complete revolutions to release the brake, the cam or gear where the target mounted must be in a ration of 1 to 5, or greater, with respect to the brake wheel, to prevent multiple signals from the sensor. Accordingly, the cost of installing the brake sensor is thus undesirably high.
The present invention is an improvement on the invention of the above-mentioned patent and provides a sensor which may be installed on the already existing equipment with a minimum of effort and without using the drive mechanism gears of the brake system or, even opening the box where the drive mechanism is protected. Furthermore, the system operates without concern of the number of brake wheel rotations. This is accomplished by providing a biased device that bears on the chain from the side and the spring force is chosen so that when the chain is taut or under tension (indicating that the brakes are xe2x80x9conxe2x80x9d) the biased device is forced by the chain to a first position. When the chain is subsequently released, the chain becomes loose (indicating that the brakes are xe2x80x9coffxe2x80x9d) and the biased device is now forceful enough to move to a second position where one or more of the chain links are moved sideways or transverse to its length. A sensor connected to the bias device senses this transverse movement to the second position and produces a signal indicating that the brake has been released and the train may safely proceed. The entire sensing mechanism may be easily installed on the railroad car without having to open or interfere with the brake drive mechanism. The sensor mechanism may be xe2x80x9cnon-contactxe2x80x9d and passive to the chain so as not to violate the integrity of the links or need to support the load that the chain experiences. Furthermore, the installation is low in cost and the bias force needed to displace the unloaded chain in a direction normal to its length is small.